(1) Field of the Invention
The present invention relates to an illumination apparatus, particularly to an indoor illumination apparatus using white light emitting diodes as light source.
(2) Description of the Prior Art
Indoor illumination technology is widely used in office, living room, study room or bedroom for ceiling lamp or wall lamp. The indoor illumination apparatus needs non-directional and uniform light beam with a large angle to provide different brightness and color temperatures according to time and space. For example, when working in office, we need cold white light to increase attention; when dining in a rest place, we need soft warm white light to relax.
There are three types of light sources in the traditional indoor illumination apparatus: fluorescent lamp, halogen bulb, and energy-saving bulb. The fluorescent lamp emits uniform light and is usually used in main indoor space. The color temperature of the fluorescent lamp is about 6500K˜3000K. The halogen bulb has a low luminance efficiency, for the halogen bulb is transparent and small, so the halogen bulb is often used in decorative art lamps. The above two bulbs both suffer from large heat, high power consumption, low luminance efficiency, and short life. The energy-saving bulb has screw or thread patterns with high luminance efficiency, but the light beam is concentrated around the bulb. The energy-saving bulb easily makes people feel dazzled and uncomfortable.
A light emitting diode (LED) is an environment-friendly light source. Compared with the traditional light source, LED is superior in life and power consumption. Furthermore, LED may be designed unlimitedly due to the small size of LED. Different color LEDs are provided for choosing, so we may switch color light to create an atmosphere and effect according to the activity or mood.
Currently, there are two kinds of LED lamps, as shown in FIG. 1 and FIG. 2.
In FIG. 1, a LED array module 100 has a plurality of white LEDs 120, adapted to the ceiling lamp or the cabinet illumination. For example, Taiwan patent No. M314819 discloses that white LED arrays with two different color temperatures are arranged on a substrate and the light beam from the LEDs is emitted out directly through the surface of the lamp. However, in such a way, the light beam from the point light sources forms light point easily but is hard to provide uniform plane light.
As FIG. 2 shows, a LED array module 200 has a plurality of red LEDs R, green LEDs G and blue LEDs B for being switched color lights optionally, suitable for a mood lamp. For example, Taiwan patent No. 509885 discloses that the light intensities of red LEDs, green LEDs, and blue LEDs are changed to amend color difference of the mixed light by adjusting width of the pulse wave. Taiwan patent No. 532699 discloses that the brightness and the color of the LEDs with different colors are adjusted corresponding to different voltages, so that the lamps may be more colorful and diversified. In addition, Taiwan patent No. 347959, 522578, I228838, I279506, I226791, and U.S. Pat. No. 6,441,558 also disclose that the white light source may be formed by mixing the lights of red LEDs, green LEDs, and blue LEDs.
Light beams of red LEDs R, green LEDs G, and blue LEDs B arranged in array may be emitted after being mixed effectively. Thus the enough distance for mixing light is needed. If the distance for mixing light is not enough, as shown in FIG. 3, a color spot 300 formed by the three interlaced colors appears on the margin of a bright region on the projection surface.
Though the illumination apparatus having red LED, green LED, and blue LED arrays may be adjusted color light from warm white to cold white, this technology currently is applied in small LED lamp to provide color change with lower brightness and also suffers from lower efficiency of mixing light and poor power saving property.
In addition, the above LED array modules 100 and 200 may also be used together in a same lamp. For example, the light emitting modules disclosed in Taiwan patent No. M332777 and No. I297757 include a first light emitting group and a second light emitting group. The first light emitting group has at least one white LED excited by fluorescent powder. The second light emitting group has LEDs emitting other colors. The color shift caused by the first light emitting group is amended by adjusting light intensity of the second light emitting group.
Most illumination technologies disclosed in the above reference patents such as Taiwan patent No. M332777, M314819, M298078, I226791 adopt a downward light source, that is, the light beam from the LED comes out directly through the lamp cover. However, the light beam from the point light source forms light point easily, and a uniform plane light is hard to be provided. Thus if the light beam enters human's eyes, glare is generated easily to make image vague and eyes tired, and the reading efficiency may be decreased.
Moreover, Taiwan publication No. 200746469 discloses a plurality of LED arrays arranged on a substrate. A LED array is regarded as main color, not limited to white, while other color LED arrays are regarded as complementary colors. The main color and the complementary colors are mixed to form white light. The average luminescent spectrum may be adjusted by the internal circuit, so as to form a color adjustable illumination apparatus. Noticeably, each LED in the case is fixed on the printed circuit board (PCB) in the form of chip rather than package. For errors of wavelength, brightness, and color come out during chip growth stage, the electrical and optical properties may change in the packaging stage. Thus, if LED in the illumination apparatus is fixed to the PCB in the form of chip, there may be still many errors in the follow-up process, and the color appearance of the LED may be affected.